Computer-assisted experimental design for the optimization of electrostatic separation processes

Electrostatic separation is a typical multifactorial process. Its efficiency depends on the characteristics of the granular mixtures to be sorted, the feed rate, the configuration of the electrode system, the applied high voltage, the environmental conditions, and so on. The aim of this paper is to demonstrate the usefulness of computer-assisted experimental design in the optimization of such a process. The example analyzed in the paper was suggested by a typical application of electrostatic separation technique in the recycling industry: the selective sorting of metals and insulating materials from chopped wire and cable waste. The objective was to maximize the benefits from the recycling of both constituents of a binary copper-polyvinyl chloride granular mixture. A preliminary set of electrostatic separation tests, performed on a custom-designed laboratory unit, guided the choice of the starting values of the parameters considered in the computer-assisted experimental procedure of process optimization. The results of a first experiment, carried out in conformity with a fractional factorial scheme, were used for the computation of the coefficients of a linear mathematical model of the electrostatic process. The model was then employed to predict the values of the operating variables for which the optimum of the process is attained. A second experiment was performed in order to confirm the accuracy of the prediction. The procedure presented in this paper and the accompanying computer programs can be easily adapted to other electrostatic process applications.